In the RFA for Molecular interaction between tumor cells and bone, one area of emphasis was that "A comprehensive analysis of genetic changes occurring between primary tumor and bone metastases and the development of a tractable system to study bone metastases are needed." This application focuses on this area of emphasis by demonstrating that we have developed a method for comprehensive genetic expression analysis between both primary prostate cancer and metastatic prostate cancer but also between prostate cancer metastases that develop in bone versus soft tissue sites. This analysis has allowed us to preliminarily identify potential genes of importance that regulate prostate cancer metastasis to bone. We hypothesize that we can identify genetic changes that are important in prostate cancer metastasis to bone and determine their functional significance in prostate cancer bone metastasis. To test this hypothesis we have developed the following specific aims: Specific Aim 1: Characterize the expression signature of prostate metastases derived from bone versus soft tissue sites. Utilizing tissue acquired through our Rapid Autopsy Program, we will identify genes that are differentially expressed in prostate cancer metastases at the gene and tissue level. Specific Aim 1A: We will utilize tissue derived from multiple bone versus soft tissue sites from a variety of patients (variable genetic background). Specific Aim 1B: We will utilize tissue derived from multiple bone and soft tissue sites from a single patient (common genetic background). Specific Aim 1C: Utilize prostate cancer cell lines grown on bone matrix versus liver extracellular matrix to look at differential gene expression. Specific Aim 2: We will investigate the function of differentially expressed genes between bone and soft tissue metastases to determine their significance to prostate cancer metastasis to bone. We will start with the FROUNT/PERICENTRIN gene, identified in our preliminary experiments. Specific Aim 2A: We will study the potential significance of genes that are differentially expressed between bone and soft tissue metastases as prognostic and diagnostic markers for prostate cancer utilizing our tissue microarrays with the corresponding clinical follow-up data. In summary, we have developed an effective paradigm for identifying and characterizing genes whose expression is altered in metastatic versus primary prostate cancers. By concentrating on genetic changes between bone and soft tissue metastases, a better understanding of the molecular biology that underpins prostate cancer metastasis should be elucidated. This knowledge could lead to the development of better biomarkers of disease progression as well as targets for therapy.